It’s possible to visit Miraflores Locks , Pedro Miguel Locks , Gaillard Cut , and the townsites of Balboa  and Ancón  in a single day. A good way to end that day is with an evening walk and a meal or a drink on the Amador Causeway  (Calzada de Amador). A quick visit to Gamboa  can be tacked on, but really exploring that area takes a second day.
A Panama Canal transit  is an all-day event; taking the Panama Railway  across the isthmus requires a half day to a full day, depending on the return trip. Isla Taboga  is better for a day trip than an overnight visit, and those planning to visit other islands can skip it altogether.
Most visitors to the Caribbean side go just for the day and return to Panama City  at night. It’s possible to take in Portobelo , the attractions near the Caribbean entrance to the Panama Canal (most notably Gatún Locks  and Gatún Dam ), and Fuerte San Lorenzo  in a single day. However, it would be a long day, with lots of driving, and it’s probably too ambitious for those relying solely on public transportation.
Consider striking either Portobelo or Fuerte San Lorenzo  off the itinerary; it’d be hard to do both. If at all possible, take the train across the isthmus at least one way. It’s the most scenic and pleasant way to make the trip.
The Panama Canal  is in the middle of a multi-billion-dollar expansion that will include two new sets of giant locks, one on the Pacific and one on the Caribbean side of the isthmus. It’s expected to be completed in 2014, but there’s unlikely to be visitor access to the work during the life of this book.
Spending the night somewhere on the Caribbean side is pretty much a must for those who want to add an outdoor activity such as scuba diving, birding, or boating to a visit.
One approach for a longer visit is to stay a night or two on Isla Grande , stopping at Portobelo on the way over and visiting San Lorenzo and the canal-area attractions on the way back to Panama City.
Rainfall is far heavier on the Caribbean than the Pacific side of the isthmus. It averages 3.2 meters in Colón, nearly twice as much as in Panama City . For those not metrically inclined, that’s more than 10 feet of rain a year. The dry season is also not as well-defined on the Caribbean as the Pacific side. In Portobelo, one of the wettest spots in Panama, it rains nearly year-round, as many a miserable Spanish conquistador learned to his dismay as he stood guard against pirates.